Impact Of Prolonged Fraction Dose-delivery Time Modeling Intensity-modulated Radiatrion Therapy On Lewis Lung Carcinoma Killing

Objective:To investigate effects of prolonged fraction dose- delivery time modeling intensity-modulated radiation therapy on tumor cellular apoptosis of Lewis pulmonary carcinoma in mice and its possible mechanisms.Method:Lewis pulmonary carcinoma models in 50 C57BL/6 male mice were prepared and randomly divided into 4 groups equally:sham-irridiated group,conventional radiotherapy group(A group),two modeling IMRT groups(B1,B2,) with different prolonged fraction delivery time(30min,45min),The mice in group A,group B1 and group B2 were irradiated with 6 MV X-rays at a dose of 15Gy(dose rate:6Gy/h).Group A were irradiated in 3 fractions over 6 min and group B1 and groupB2 were irradiated in 5 fractions over 30min and 45 min.All the mice were executed at 24 hours after irradiation respectively.By using the methods of TUNEL and immunohistochemical staining,the changes of apoptosis index(AI) and level of Bcl-2,Bax protein expression in tumor tissues were examined.Results:1.Differences of apoptosis index of tumor tissues between groups had notable statistical significance(P＜0.01).In sham-irridiated group apoptosis index was the lowest,while in A group apoptosis index was the highest,sham -irridiated group and irridiated groups had notable statistical significance(P＜0.01).Compared with A group,the AI of B1 group and B2 group decreased significantly,and the diference had notable statistical significance(P＜0.01).Compared with B1 group,the AI of B2 group decreased, But the difference had no statistical significance(P＞0.05).2.Differences of the expression of Bax protein between groups had notable statistical significance(P＜0.01). Compared with sham -irridiated group the expression of Bax protein of A group,B1 group and B2 group all increased significantly,and the diference had notable statistical significance(P＜0.01).the expression of Bax protein in A group was significantly higher than that in B1 group(P＜0.05)and B2 group(P＜0.01).Compared with Blgroup,the expression of Bax protein in B2 decreased,the diference had statistical significance(P＜0.05).3.Differences of the expression of Bcl-2 protein between groups had notable statistical significance(P＜0.01).Compared with sham -irridiated group the expression of Bcl-2 protein in A group and B1 group all decreased significantly,and the diference had notable statistical significance(P＜0.01),The expression of Bcl-2 protein of B2 group Was also lower than that of sham-irridiated group,But the difference had no statistical significance(P＞0.05).The expression of Bcl-2 protein in A group was the lowest,Compared with B1 group and B2 group the diference had notable statistical significance(P＜0.01).Compared with B2 group,The expression of Bcl-2 protein in B1 decreased,but the diference had no statistical significance(P＞0.05).Conclusion:Ionizing radiation can induce apoptosis and up-regulate the expression of Bax protein and down-regulate Bcl-2 protein in lewis lung carcinoma.The apoptosis induced by irradiation maybe depend on the regulating of Bax protein and Bcl-2 protein after irradiation.Prolonged fraction dose- delivery time modeling intensity-modulated radiatrion therapy induced apoptosis index decrease.The degrees of the expression reducing of Bcl-2 protein and the expression lifting of Bax protein decreased,Which caused the decreas of lewis lung carcinoma cell apoptosis.